In the fields of wellbore construction and intervention, swellable tools are used to provide isolation between two regions in an annulus formed between an exterior surface of a tubular and an interior surface of well casing or a wellbore. A swellable member is formed from an elastomeric material selected to swell when placed in certain fluids. Where the swellable member swells in oil, the member may comprise an oleophilic polymer such as ethylene propylene diene monomer rubber (EPDM). Where the swellable member swells in water, the member may comprise a polymer such as an N-vinylcarboxylic acid amide-base cross-linked resin and a water swellable urethane in an ethylene-propylene rubber matrix.
Hybrid swellable materials have been developed that swell in both oil and water. Such hybrid swellable materials typically use EPDM or other similar oil-swellable materials mixed with acrylate copolymers, commonly designated as super absorbent polymers (SAPs), that swell in water. Other types of swellable materials have been used, including various clays, salts, and other absorbents. Swellable materials are relatively recent in the oil and gas industry, and no industry standard exists.
However, SAP-based hybrid swellable materials have vastly different swell rates in fresh and salt water, because of the ionic nature of the SAP. The industry has desired a swellable material that will perform better in salt water conditions. In addition, SAPs have a tendency to extrude from the elastomer matrix, and a material that would reduce extrusion from the elastomer matrix would be desirable.